Web robot is an important Internet software technology used in a variety of Internet application software which includes search engines. As Internet continues to grow, implementations of high performance Web robots are urgently demanded. For this, researches specially geared toward performance scalability of Web robots are required. Hoover, because researches are focused mostly on addressing issues related to commercial implementations, scientific researches and studies are not still made on the performance scalability. In this research, Ive choose a Web robot model implemented by fork-join based. multiprocesses. With respect to the model, we evaluate the effect on the collection efficiency that the timeout values set to requests from Web robots to Web servers have. Also, we analysed the behaviors of Web robots by comparing the execution time between the URL extraction and the uniqueness checking for the extracted URLs. as well as by comparing between the computation time and the network time. Based on the analysis result, we suggest the direction for the design of high performance Web robots.